In the related art, aluminum (Al) widely used as a wiring film of a flat panel display such as a liquid crystal panel or an organic EL panel and as a wiring film of a touch panel or the like. Recently, the size (width) and thickness of a wiring film has been reduced, and there has been a demand for a wiring film having a lower specific resistance than that in the related art.
Along with the above-described reduction in the size and thickness of a wiring film, a wiring film formed of copper or a copper alloy, which is a material having a lower specific resistance than Al, has been provided.
However, a Cu wiring film which is formed of copper or a copper alloy having a low specific resistance has a problem in that it easily discolors in a humid atmosphere. In a case where a copper alloy containing a large amount of additive elements is used to improve weather resistance, the specific resistance increases.
Therefore, for example, PTL 1 discloses a layered film in which a protective film formed of a Ni—Cu—(Cr, Ti) alloy is formed on a Cu wiring film; and a sputtering target for forming the protective film. This protective film has higher weather resistance than copper and thus can suppress the discoloration of a surface of the layered film even when the layered film is stored in the air.